Technical Field
The present invention relates to an ultrasonic image processing apparatus, and in particular to a technique for improving resolution or quality of ultrasonic images.
Background Art
An ultrasonic image processing apparatus is formed, for example, as an ultrasound diagnosis apparatus or an information-processing device. In the information-processing device, image data provided from the ultrasound diagnosis apparatus are processed. In the following, an ultrasound diagnosis apparatus will be described. An ultrasound diagnosis apparatus is an apparatus which transmits and receives ultrasound to and from a living body, and which forms an ultrasonic image based on received information acquired by the transmission and reception of the ultrasound. As an ultrasonic image, a two-dimensional tomographic image, a two-dimensional bloodstream image, a three-dimensional image, or the like are known.
More specifically, an imaginary scan plane is formed by electronic scanning of the ultrasonic beam in a living body. With this process, a received frame (received frame data) corresponding to the beam scan plane is acquired. The received frame comprises a plurality of beam data sets arranged in a beam scan direction, and each beam data set comprises a plurality of echo data sets arranged in a depth direction. In other words, the received frame comprises a two-dimensionally placed group of echo data (echo data array). An individual echo data point is an element of the received frame, and is generally called a “pixel”. An element of a display frame to be described later is also generally called a pixel.
Each of the pixels of the received frame has an address conforming with a transmission/reception coordinate system (a polar coordinate system in the case of electronic sector scanning). In order to convert the received frame into a display frame; that is, in order to convert from the transmission/reception coordinate system to a display coordinate system (orthogonal coordinate system), the ultrasound diagnosis apparatus is equipped with a scan converter (JP 2003-299651 A). In addition to the coordinate conversion function, the scan converter has an interpolation processing function, a frame rate adjusting function, or the like.
In order to improve the quality of the ultrasonic image, it is desirable to increase the resolution or density of the received frame. However, if the number of beam data sets of one received frame (echo data density) is increased, the received frame rate would be reduced. An inter-frame interpolation process or an inter-line interpolation process may be applied to the received frame, to increase the pixel density or the line density. However, in the related art, a simple linear interpolation process has been used as such interpolation processes, and, therefore, even though an amount of data appears to be increased, the quality of the ultrasonic image cannot be sufficiently improved.
In beam scanning methods such as sector scanning, convex scanning, radial scanning, etc., a beam array of a fan shape or a radial shape is formed, and the beam spacing is widened for deeper sites. In the scan converter described above, a large number of pixels required for the display frame are generated by interpolation calculation. Therefore, a large number of interpolation pixels are embedded in a deep portion in the display frame. Thus, in such a deep portion, although pixel insufficiency does not occur, there has been a problem in that the image is blurred. More specifically, there has been a problem in that the image shifts or deforms in the beam scan direction. A similar problem occurs when a three-dimensional image is formed.